Stabilized regenerative circuits



Feb. 23, 1943. R A, WEAGANT 2,312,139

STABILIZED REGNERATIVE CIRCUITS Filed June 11, 1941 ALHAMA www" INVENTOR Patented Feb. 23, 1943 s'mnnrzan REGENERATIVE ocm'rs Roy A. Weagant, Douglaston, N. Y., assigner to Radio Corporation ot America, a corporation of Delaware Application June 1li, 194.1, Serial No. 397,536

Claims. (CL 179-171.)

My present invention relates to regenerative systems, and more particularly to a novel, and improved, method of stabilizing regenerative transmission networks.

As is well known, regenerative amplifier circuits may often give rise to slight instabilities due to various factors. In the iirstplace variations in circuit constants, particularly where small trimpresent invention to provide a method of, and

means for, stabilizing regenerative circuits wherein a special control electrode is employed in the regenerative tube to provide a reactive effect across the regenerative output circuit, and the reactive eil'ect being such as slightly to mistune the output circuit when unstable conditions arise.

Another important object of the invention may be stated to reside in the provision of a regenerative network, particularly adapted to provide a highly amplified carrier voltage for use in a demodulator employing an exalted carrier voltage,

utilizing a tube provided with a special control K grid which has applied to it signal voltage which is in Aquadrature with thev signal voltage applied to the normal signal control grid whereby a capacity effect is simulated across the regenerative output circuit, and the said capacity eiiect being of suiiicient magnitude slightly to detune the output circuit in response to variations in the transconductance oi` the regenerative tubelsuicient to cause instability. y

Still other objects of the invention are to improve degenerative ampliiier circuits, and more especially to provide a stabilized regenerative circuit which is not only reliable and eicient in operation but which is economically manufactured and assembled.

The novel features which I believe to be characteristic of my invention are set forth in particularity in the appended claims; the invention itself, however, .as to both its organization and methodof operation will best be understood by reference to the following description taken in connection with the drawing in which I have indicated diagrammatically a circuit organization whereby my invention may becarried into eilect.

In the drawing:v 4 Fig. l shows a circuit diagram of a regenerative A circuit embodying the invention,

Fig. 2 graphically illustrates the functioning oi the invention.

While the present invention is explained in connection with the second detector circuit of a receiver of the type shown in my application Serial No. 335,892, led May 18, 1940, now Patent No. 2,243,141 dated May 27, 1941, yet it will be understood that the stabilized regenerative ampliiler may be employed in any other circuit suitable for utilizing regeneration. Brieiiy, in the aforesaid application it has been shown that a highly improved rejection of interference can be secured if there is injected into the demodulator circuit highly amplied oscillations derived fromv the sigynal energy and having substantially all modulation side bands removed. The phenomenon has been termed phase detection, and the circuit involved is generally as shown in Fig. 1. The superheterodyne converter tube plate includes the resonant output circuit 3 4, and the latter is tuned to the operating intermediate frequency (I. F.) lvalue of, for example, 425 kilocycles (kc.) The usual networks of a superheterodyne receiver precede the circuit 3-4.

The demodulator, or second detector, comprises the double diode tube 6 having a resonant input circuit. The latter consists of coil 'i coupled to primary coil li. The condensers 8 and 9 are oi .equal value, and are in series across coil 1. The

input circuit is tuned to the operating I. F. value. The anodes of the diode are connected to opposite sides of'input circuti 1-8-9. The diode cathode is connected to the mid-point of coil 1 through load resistor iil'which is properly by-pa'ssed for I. F. currents by a condenser. The cathode end of the load resistor may be grounded; and audio voltage across the load is utilized in any well knOWn manner.

The I. F. voltage for providing the exalted, or highly amplied,.vcarrier voltage is takenoi through condenser 5 from' the primary circuit l 3 4. The sharply 'tuned regenerative network,

including tube T,coil 40 and coil 5I., substantially removes all the modulation side bands from the carrier; actually there might be components up to 400 cycles remaining on the I. F. carrier. The

' exalted carrier lenergy is applied to the junction cation it is highly desirable to use a full wave rectiiier as the demodulator, and to apply the exalted carrierin the balanced state shown. It is not believed necessary for the purposes of this application to explain the demodulation action any further, reference is made to my aforesaid application and Fig. 4 thereof for a specific explanation.

'I'here are various factors which may give rise to a certain degree of instability in the regenerative circuit. These may be variation in circuit constants; variation in the characteristics of dif-v ferent tubes due to ordinary manufacturing differences or aging eii'ects; variation in power supply voltage. One useful and advantageous step that can be taken to improve stability is to employ permeability tuning in the tuned circuits, and thus eliminate adjustable condensers. Hence, it is to be understood that the well known adjustable powdered iron core inductanceskmay be utilized for tuning.

'Ihe regenerative tube per se is a pentagrid tube T, say of the SAB type, which has a cathode 2l, a plate 2l and ilve intermediate grids 22, 28, 24, 25 and 26. The I. F. energy is fed to grid 22. The grid 22 is connected to ground by leak 30; cathode 20 is connected to ground by the usual self-biasing resistor R shunted by an I. F. by-pass condenser. Grids 23 and 25 are connected to a point of positive potential, and are, therefore,

positive screen grids. The plate 2| is connected v to asource of positive voltage through coil 40 shuntedby a tuning condenser 4l. The plate circuit is resonated to the operating I. F. value, and is reactively coupled to circuit i 3I4 to provide sharp tuning.

' Grid 24 is connected to the cathode through series coils B and BI. Coil 50 is coupled to the upper part of coil 40, the arrow therethrough indicating adjustable coupling. Coil i is reactively coupled to the lower part of coil 4l, the coupling also being adjustable. The purpose of the coupling lli- 4U is to neutralize the eiIect of inherent feedback between coils 4 and 1. 'I'he coupling 56-40 is degenerative, and exactly neutralizes regenerative coupling between coils 4 and I due to the regenerative tube.

Whereas in my previous application regenerative feedback was provided by a capacity coupling between the plate and grid of the regenerative tube, in this case coil 5I is inductively coupled to coil 4l to provide the required regenerative feedback. 'I'he coil 5I is connected in the opposite direction to coil l0. Grid 24 has, therefore, a dual function: to eliminate an undesired coupling, and to provide a controllable and desired coupling between the output circuit 40-4l and the ,inputV circuit 2 4. Normally these circuits are tuned to the I. F. value.

The voltage induced in coil 5l will be in exactly opposite phase to the voltage across coil 40 at resonance.' Assuming the use of permeability tuning to eliminate variation in circuit constants, all other causes of variation will show up in a variation of the transconductance of tube T. An

increase in this' quantity will cause oscillation; a decrease will cause tube T to become less regenerative. Stabilization, therefore, requires a variable eifect which is dependent upon transconductance, and acts in the reverse sense to the regenerative ei'fect.` v

This reversely-acting effect is provided by grid 2C connected to the upper end of coil 2. The

vlower end of the coil is connected to the cathode.

and the coil is loosely coupled to input coil 4.

tuner.

Condenser I tunes coil 2 to the operating I. F. value. Here, again, coil 2 may be a permeability The voltage on grid 26 will be in quadrature with the voltage applied to input grid 22; the quadrature voltage may lead or lag. Assuming that it is a lagging voltage, then there will be` a component of the plate current in quadrature with that due 1501 grid 22 and it Wl'J be leading.

It is, therefore, equivalent to acapaity in shunt with condenser/4|, and the tuning'of circuit 40-4! will in part be determined by the magmtilde of the simulated capacity. This magnitude,

in turn, will be determined by the coupling between coils 4 and 2 which is constant, 'and by the transconductance; of tube T which is variable. Hence, it will be seen that there has been provided a means for automatically adjusting the resonant frequency of the plate circuit til- M in response `to variations in transconductance oi' tube T.

Fig. 2 is a curve which represents variations in transconductance (g) plotted against variations causing changes in g. The curve is drawn in linear form, but might be of any other form. Letv it be assumed that point A ofthe curve represents the average value of y for a given type of tube, while B represents the maximum value that it can conceivably assume under any operating conditions that may be met in practice. Point C on this curve represents a very small value of transconductance that can occur. In this latter case, tubes which are definitely inoperative or worn out are excluded, b'uttubes which have less than normal value' of g when new, or are reduced in effectiveness by long service, are included. Point D represents a value of transconductance which is somewhat less than that of C.

Resistance R is assumed to be variable over small range and with a tube T in place, it is so adjusted that the value of g corresponds to point D on the curve of Fig; 2. The input circuit 3 4 retuned while the circuit Sli-5|, previously assumed to be open, is adjusted in the manner already indicated. Assuming that the tube is adjusted to the point just below oscillation, with the transconductance corresponding to the point D, any increase in this quantity in the direction of C, A, B will cause an increase in the feedback,-

and, therefore, would' result'in oscillationfproduction unless compensated for. At the same time, however,v the quadrature current due to circuit |-2 increases, vwhich means that the.

capacity in circuit 40--4I increases, and it is, therefore, detuned. This detuning action will immediately reduce the feedback, and produce a compensating action. The magnitude of the detuning can be properly adjusted by adjusting the coupling betweenlcoilsl and 2.

It is now apparent 4that as the transconductance increases, Vthe `detuning .eii'ect increases. Under normal operating conditions, the transconductance would haye a value, indicated at A, and the plate circuitwould be'somewhat detuned. rf the une' voltage' dropped or the tube began to age, vor both oi'1 these effects occur, the value of 'y will move toward points C and D, and the plate circuit would then be more lnearly in tune with the operating I; F. value.;v Qn .the other hand, ifthe line voltage became abnormally high, or if atube asiaiee were substituted for T with an abnormally high value of g, then operating conditions would move toward the direction of B and the plate circuit would be detuned to a greater extent.

It is to be noted that the smaller the value of the condenser 4I, the greater will be the effect ldue to circuit i-2. The suppressor grid 28 which is used to producer the quadrature current has a controlling action which is small relative to the grid 22. iii more powerful quadrature actionis obtainable by interchanging grids 24 and 28. The amount of detuning necessary to produce the control action described above will be extremely small. In addition to the rapid falling ofi in intensity which will take place, there will be a shift in the phase angle of the voltage applied to the regenerative grid which will produce an additional reduction of the feedback. By making resistor R adjustable, it is possible to control thel grid bias of grid 22, and, hence, the transconductance of tube T. When the circuits are adjusted at the prope'r point for regeneration, a very slight mistuning of circuit t-l will prevent it from oscillating, even with a large increase of the transconductance of the tube. It is, therefore, seen that only a very slight detuning action will be necessary to produce the required control action.

f It is .to be clearly understood,- of course, that the present invention is in no way limited to the particular use shown. In other words, the sta- -bilized regenerative circuit shown herein may be used in any situation where regenerative circuits are employed. Essentially what has been disclosed herein is a regenerative circuit which comprises a tube having at least one control electrode functioning to provide regenerative action, and a second control electrode cooperating with the input circuit to provide a reaction eilect in the regenerative output circuit sufiicient slightly vto detune the output circuit thereby to prevent oscillation production should the transconductance of the regenerative tube increase for any reason beyond a desired normal operating condition representative of stabilized regeneration. If desired,

the circuit i-Z may be omitted, and the gridl 26 may then be connected directly to I-M i'or the voltage thereof.

While I have indicated and described a system for carrying my invention into effect, it will be` yapparent to one skilled in the art that my inven- V tion' is by no means limited to the particular organization shown and described, but that many modiilcations may be made without departing from the scope of my invention,l as set forth in the appended claims.

What I claim is: l

l. In combination with a tube' provided with at least a cathode, a wave-input electrode, a control electrode, an output electrode, a wave input circuit connected between said input elec-l trode and said cathode,` a wave output circuit connected to said output electrode, means regenrratively coupling said control electrode to said utput circuitrneans,v reactively coupled to said o \input circuit, for controlling electrons flowing to said utput electrode and providing a reactive effeet ac ss said output circuit whose magnitude is varied W\ith\`the transconductance of said t ube.

2. In combinatiorpwi-th a'tube provided with at least a cathode, a wavesiniriut electrode, a control electrode, an output elect ed@ a wave input circuit connected between said inputtelxectrode and said cathode, a wave output circui @nected to said output electrode, means regenerati ely guat least a cathode, a wave input electrode, a control electrode, an output electrode, a wave input circuit connected between said input electrode and said cathode, a wave output circuit connected to said output electrode, means regeneratively coupling said control electrode to said output circuit, means, reactively coupled to said in put circuit, for controlling electrons flowing to said output 4electrode and providing a reactive effect across said output circuit whose magnitude is varied with the transconductance of said tube, said last means consisting of an auxiliary control electrode disposed between said control electrode and output electrode, and a resonant circuit, tuned to the frequency of applied waves,

- reactively coupling said auxiliary electrode. y 4. In a regenerative signal transmission circuit, a tube provided with at least a cathode, an 30 output electrode and atleast three control grids arranged in successive order in the electron stream vbetween the cathode and output electrode, a signal input circuit connected between the first grid and cathode, a signal output circuit connected between the output electrode and cathode, means regeneratively coupling the second grid to said output circuit to provide a desired regenerative feedback action, a `third signal circuit lconnected to the third grid, said third signal circuit being reactively coupled to said signal input circuit in' such a manner that -a reactive effect is produced across said output circuit which is sufficient slightly to 'cletune the output circuit in response to an increase in the transconductance of said tube above a predetermined transconductance value. 5. In combination with a tube provided with at least a cathode, a wave input electrode, a control electrode, an output electrode, a wave input circuit connected between said input electrode vand said cathode, a wave output circuit connected to said output electrode, means regeneratively coupling said control electrode to said output circuit, an auxiliary grid in said tube, reactively coupled to said input circuit, for controlling electrons flowing to said output electrode and providing a reactiveeflect across said output circuit whose magnitude is varied with thetransconductance of said tube.

cuit, an electron discharge tube provided with at least a cathode, a plate and at least three control grids-,arranged in successive order in the electron stream between the cathode and plate, a signal input circuit connected between the first grid and cathode, a signal output'circuit tuned to the input signal connected between the plate and cathode, means regeneratively coupling the second grid to said output circuit to provide a desired regenerative feedback action, a third signal circuit tuned to'said input signal connected to the third grid, said third signal circuit being reactively coupled to said signal input circuit.

7. In a high frequency regenerative amplifier system, a 'tube provided with input and output input circuit to said 6. In a regenerative signal transmission vcir-- electrodes, a high frequency input .circuit coupled to the input electrodes, `a high frequency output circuit coupled tothe output electrodes, a special regeneration grid in said tube, means providing regenerative feedback between the output circuit and the specialgrid, and means including an auxiliary electrode in said tube, responsive to variations in transconductance of said tube from a. predetermined normal operating value, for regulating the current flow in said output circuit in a sense to stabilize the feed" back.

8. In a regenerative signal amplifier system provided with signal input and output circuits, a tube having input and output electrodes coupled to said input and output circuits respectively, a control electrode in said tube for regeneration,- means providing regeneration between the output circuit and said control electrode, an auxiliary electrode located within said tube, and means reactively coupling said auxiliary electrode to said input circuit in such a manner that signal voltage applied to the auxiliary electrode is `.in quadrature with the signal voltage applied to the input electrodes. l

9. In a regenerative signal amplifier, a tube-- provided with at least a cathode, an output electrode and at least three control grids arranged in successive order in the electron stream between the cathode and output electrode, a signal input circuit connected between the 'first grid 'and cathode, a signal output circuit connected trodes, a high frequency output circuit coupled to the output electrodes, means providing regenerative feedback between the output circuit and the special electrode, and means operativel to control the electron ow in said tube, and responsive to variations in transconductance ofsaid tube from a predetermined normal operating value, for regulating the current ow in said=out put circuit in a sense to stabilize the feedback.'

ROY A. WEAGANT. 

